This invention relates to a filter circuit.
A conventional circuit as shown in FIG. 1 is primarily used to eliminate a DC component included in an output of an audio amplifier. In this circuit, a DC component included in an output of an amplifier 1 is blocked by a capacitor 2 to permit only an AC component to be supplied through an output terminal 3 to a load 4 such as a loudspeaker. When the impedance of the load 4 is low, it is necessary that the capacitance of capacitor 2 be made greater to assure a good low frequency response. It is therefore necessary to use a capacitor of larger size. However, a large-capacitance and large-sized capacitor is poor in its electrical performance.
FIG. 2 shows a highpass filter circuit. Even in this circuit a capacitor 5 of greater capacitance is necessary to permit a signal of very low frequency to be passed.